1. Field of Invention
This invention relates to a hot rolling method in which finish rolling is continuously performed. This invention particularly relates to a method for setting operating conditions for hot rolling facilities, which is capable of speedily and accurately performing setting changes regarding rolled material for which was planned endless rolling, wherein a preceding piece of material and a subsequent piece of material are joined each other at the entering side of a finishing mill, to batch rolling, wherein rolling is performed without joining the preceding piece of material and subsequent piece of material, or performing setting changes from batch rolling to endless rolling.
2. Description of Related Art
Conventionally, in hot rolling process, slabs are heated in a reheating furnace, and the slab extracted form the reheating furnace is subjected to rough rolling, and then finish rolling is performed for each roughed sheet bar, i.e., a batch rolling operation has been performed to manufacture steel strips, such as thin articles. However, in recent years, so-called endless rolling operation has been performed to manufacture steel strips, such as thin articles. In these operations, the tail end (rolled) of a preceding material is joined to the head end (rolled) of a subsequent material between a roughing mill and finishing mill, which is repeatedly performed so as to continuously perform finish rolling of the preceding material and the subsequent material.
FIG. 4 schematically shows an apparatus 10 for endless rolling. During the endless rolling operation, the tail end 12 of the preceding (downstream) material 14 and the head end 16 of the subsequent (upstream) material 18 are joined to each other at a sheet bar joining machine 30 provided between a 3-stand roughing mill 20, for example, and a 7-stand finishing mill 40, for example, so that finish rolling is continuously performed with the preceding material 14 and the subsequent material 18 being joined. A strip shear 50 for cutting the rolled material is provided downstream from the finishing mill 40, and multiple coilers 60 (two are shown) are provided downstream from the strip shear 50, so that the rolled material is subjected to finish rolling in the state in which the preceding material 14 and the subsequent material 18 are joined and is cut by the strip shear 50 into lengths which the coilers 60 can take up, with the rolled material preceding the cutting point, and the rolled material following the cutting point, being taken up on separate respective coilers.
Continuous finish rolling can be performed in the state in which the preceding material 14 and the subsequent material 18 are joined to each other by such an endless rolling operation, so there are no inconsistent portions at the head and tail ends in the finish rolling of individual sheet bars as with batch rolling, and stable rolling can be performed over the entire length of the rolled material. Thus, this arrangement is suitable for the rolling of rolled material for which the passage of inconsistent portions is difficult, such as with thin articles.
Operation condition (OC) settings for the facilities within such a hot rolling line are made by computer, as shown in FIG. 5. That is, for each slab (material to be rolled), product information (PI) (slab thickness, slab width, product thickness, product width, specifications, etc.) are inputted to an on-line computer 70, the on-line computer 70 sets the operating conditions (OCI) (tension between stands in the finishing mill, coiling tension, rolling speed, rolling temperature, draft schedule, conditions for cooling rolled material, etc.) for initial settings for the hot rolling facilities based on the slab information, and these operating conditions (OCI) for initial settings are sent to a process computer 72. Once the slab is placed on the rolling line, the process computer 72. Once the slab is placed on the rolling line, the process computer 72 reads in rolled material information (IRM), such as detection values (temperature, plate thickness, plate width, etc.) from detectors positioned at various locations on the rolling line. In FIG. 5, these detectors are the detector 24 at the exit side of the roughing mill 20, the detector 32 at the exit side of the sheet bar joining machine 30, and the detector 44 at the exit side of the finishing mill 40. The process computer 72 also reads in actual operating data, including the rolling load at the drafting devices 22 of the roughing mill 20 and at the drafting devices 42 of the finishing mill 40, of the facilities for continuous hot rolling. In the embodiment shown in FIG. 5, these facilities include the roughing mill 20, sheet bar joining machine 30, finishing mill 40, strip shear 50 and coiler 60. The process computer 72 calculates the operating conditions (OC) for the facilities downstream from the current position of the rolled material, so that the rolled material is rolled to the product specifications provided to the on-line computer 70, based on such rolled material information. Then, operating conditions signals based on the calculation results are sent to the facilities, thereby running these facilities.
For example, for batch rolling operations, the calculation of the operating conditions (OC) of the finishing mill 40 by the process computer 72 is performed as follows. At the stage that the rough rolling is completed at the roughing mill 20, the rolled material information (IRM) relating to the dimensions and temperature of the roughed sheet bar is detected by the detector 24 at the exit side of the roughing mill 20, or is calculated based on the actual operating data from the roughing mill 20, and operating conditions (OC) for the finishing mill 40 (load for each stand, mill gaps, circumferential speed for the reduction rollers, etc.) such that the finish rolling is executed under the finishing operating conditions (OC) sent from the on-line computer 70, based on the rolled material information.
On the other hand, in the endless rolling operation, the process computer 72 calculates the operating conditions (OC) for the finishing mill 40 regarding the subsequent material 18, after the preceding material 14 is joined to the subsequent material 18 at the sheet bar joining machine 30.
However, in some cases, rolled material for which endless rolling was planned must be switched to batch rolling, due to reasons such as operating problems occurring, e.g., malfunctioning of the sheet bar joining machine 30.
In this case, the operating conditions (OC) settings for the finishing mill 40 regarding the rolled material for which endless rolling was initially planned are based on the operating conditions (OC) provided from the on-line computer 70 assuming that endless rolling is to be performed. Accordingly, in the event that batch rolling is performed with the setting values for the operating conditions (OC) for endless rolling maintained as they are, the target product dimensions cannot be attained. Accordingly, in the event of performing batch rolling for rolled material for which endless rolling was initially planned, the operating conditions (OC) for the finishing mill have been manually changed by the operator to carryout the batch rolling.
However, when such setting changes in operating conditions (OC) are made by manually, not only are the operations extremely complicated, they must also be carried out in the short time period between the tail end 12 of the preceding material 14 completely passing through the finishing mill 40, and the finishing mill 40 biting the head end 16 of the subsequent material 18. Accordingly, there have been problems, such as changes in the settings of the operating conditions (OC) not being made accurately, or not being made in time, resulting in operating problems, or in not attaining the target rolled product dimensions, and consequently producing defective coils.
Japanese Unexamined Patent Publication No. 6-297018 discloses an arrangement in which material fracture detection is performed for the connection of materials when performing continuous hot rolling, and based on the detection of material fracture, the transport speed of the material upstream of the fracture point is temporarily reduced so as to create a spacing between the material upstream of the fracture point and the material downstream of the fracture point, and the settings for the finishing mill are switched from the endless rolling setting method to the batch rolling setting method, thereby eliminating miss rolling at the time of biting with the finishing mill. However, this Publication does not disclose any method for switching from endless rolling to batch rolling in the event that some sort of anomaly occurs before, or at the time of, joining the materials.
The above description pertains to problems regarding the finishing mill 40 in switching material to be rolled, for which endless rolling had been planned, to batch rolling. However, there are similar problems for facilities other than the finishing mill 40, such as the rolled material cooling equipment (not shown) or coilers 60, for example, provided downstream from the finishing mill 40.